The present invention relates to soft stretch yarns which, by means of their outstanding crimpability, can confer soft stretchability on fabrics, and to the fabrics formed using said yarns.
Synthetic fiber fabrics are outstanding in their durability, easy-care characteristics and the like when compared to natural fiber fabrics and semi-synthetic fiber fabrics, and are widely used. However, when compared to natural fiber fabrics and semi-synthetic fiber fabrics, they are inferior in terms of aesthetic appearance and handle, so various improvements have been made in the past. One approach has been to imitate natural or semi-synthetic fibers. On the other hand, in terms of appearance and handle, improvements have been actively pursued in recent years directed towards the synthetic fibers themselves, quite distinct from natural fibers and semi-synthetic fibers. Amongst these, considerable research has been conducted to broaden the areas where natural or semi-synthetic fibers are poor and synthetic fibers superior. One such major area is the characteristic known as stretch.
With regard to the conferring of stretchability, hitherto there has been employed for example the method of mixing polyurethane fiber into a woven fabric to impart stretchability. However, polyurethane fiber has problems such as the hardness of handle inherent in the polyurethane itself, and a lowering of the handle and drape of the fabric. Moreover, polyurethane is difficult to dye by the dyestuffs employed for polyester and, when used in combination with polyester fiber, not only is the dyeing process complex but also dyeing to a desired color is difficult.
Hence, as a method which does not use either polyurethane fiber or false-twist textured yarn, polyester fibers employing side by side polymer conjugation have been variously proposed.
For example, in JP-44-2504 and in JP-A-4-308271, there are described side by side bicomponent fibers of polyethylene terephthalate (PET) with different intrinsic viscosities or intrinsic viscosities; and in JP-A-5-295634 there is described a side by side bicomponent fiber of homo PET and copolymer PET of higher shrinkage than the homo PET. When such polyester fibers with latent crimpability are used, it is indeed possible to obtain a certain degree of stretchability but there is the disadvantage that a high stress is generated when the fabric is stretched, that is to say there is a strong feeling of tightness and a hard fabric is formed. Moreover, with side by side bicomponent fibers of this kind, there is the problem that the capacity to manifest crimp in a constrained state within a woven material is low, or the crimp is readily permanently distorted by external forces. Side by side bicomponent fiber yarns do not utilize stretchability based on a substrate polymer such as a polyurethane fiber but, in order to provide the stretchability, utilize the crimp manifested as a result of the difference in shrinkage between the polymers in the conjugate fiber, with the polymer of higher shrinkage forming the inside of the crimp. Hence, it is thought that the aforesaid problems arise when, for example, heat treatment is carried out with the shrinkage of the polymer restricted as in the case when present in a woven fabric, and heat setting takes place in this state, so that the shrinkage capacity beyond this constrained state is lost.
Furthermore, side by side bicomponent fiber yarns employing polytrimethylene terephthalate (PTT) or polybutylene terephthalate (PBT), which are polyesters with slight stretchability, are described in JP-43-19108, but in Example 15 of that publication it states that the power required for stretching is large. In fact, when estimated from the finished yarn counts of the heat treated fabric, in Example XV-d the stress generated at 30% stretch is rather high at 60xc3x9710xe2x88x923 cN/dtex or more, and so there is a strong sense of tightness. In addition, when we conducted follow-up experiments, we found disadvantages in that the Uster unevenness (U%) was poor and dyeing unevenness when in the form of fabric was considerable.
The present invention aims to resolve the problems of a strong feeling of tightness and coarsening of the fabric, and the problems brought about by yarn unevenness, which are problems associated with conventional side by side bicomponent fiber yarns, and to provide soft stretch yarns which can give fabrics with more outstanding soft stretchability and more outstanding uniformity of dyeing than hitherto, together with the fabrics produced from said yarns.
The present invention provides, according to one aspect, a yarn (Y) substantially comprising (and preferably consisting of) polyester fibers, which yarn (Y) is characterized in that, following heat treatment, the yarn has a stress at 50% yarn stretch of no more than 30xc3x9710xe2x88x923 cN/dtex and, at the same time, a percentage recovery of at least 60%. Preferably, the Uster unevenness is no more than 2.0% and the diameter of the crimp is no more than 250 xcexcm. It is also preferable for the fibers to be conjugate, more preferably multi-segment (side by side) or a core sheath (ie. having an eccentric cross section) fibers having at least two components each of different respective polyesters.
According to a method aspect, the invention provides a method (A) of producing a yarn by spinning a yarn of conjugate fibers comprising two types of polyester in which, preferably, PTT is one component, at a take-up velocity of at least 1200 m/min, drawing at a drawing temperature of 50-80xc2x0 C. and a draw ratio which gives a drawn fiber elongation of 20 to 45%, and then heat setting.
According to other method aspects, the invention provides respective methods (B) and (C) of providing a yarn, in which method (B) a yarn of a conjugate fiber comprising two types of polyester is spun from a spinneret and taken up at a take-up velocity of at least 4000 m/min by providing a non-contact heater between the spinneeeret and a godet roller and in which method (C) a yarn of a conjugate fiber comprising two types of polyester is spun at a take-up velocity of at least 5000 m/min.
Each of the above methods may be utilized to produce a yarn (Y) having the above characteristics and thereby allow a soft stretch yarn to be obtained which at least partially remove the abovementioned problems.